Melanin is a class of naturally occurring polymers that are responsible for the coloring of natural tissue, inter alia, skin and hair. Depending upon the chemical make-up of the particular polymer, the resulting pigment can have a wide range of colors, i.e., very light to very dark (for example, black). In keratin-containing fibers such as human hair, melanin is produced together with the hair-forming cells in the hair bulb located at the root of the hair fiber. When new hair cells are formed, older cells move upward and form the fiber shaft which extends above the skin surface, for example, the scalp. Hair comprises a central cortex containing the melanin and an outer cuticle. The particular composition of the cortex provides keratin-containing fibers with their particular physical properties, inter alia, whether the fibers are straight or are curled.
The dead cells which comprise the keratin-containing fibers of hair are proteins that comprise high concentrations of cystine which is the natural crosslinking of two cysteine amino acids located on different protein chains via a disulfide bond. The strength and rigidity of hair is a result of a high concentration of these crosslinks.
Humans, as they grow older, produce less and less melanin resulting in hair developing a gray to white color. Dark keratin-containing fibers can be deliberately lightened by chemical treatment, for example, by contacting the fibers with an oxidizing agent that breaks down the polymeric backbone of melanin. “Bleaching” of human hair to lighten the color or hue of the fibers can be accomplished by contacting the fibers with any one of several oxidizing agents, inter alia, hydrogen peroxide, potassium, sodium or ammonium salts of perborate or percarbonate, persulfate and percarbamide.
During the process of dyeing, tinting, or otherwise coloring keratin-containing fibers, oxidizing agents are used to produce the final colorant from an admixture of colorant precursors. These precursors are typically low molecular weight molecules that diffuse into the interstices of the fibers where they react with one another due to the presence of an oxidative catalyst, for example, hydrogen peroxide. Colorant formulations are typically comprised of one or more agents capable of swelling the keratin-containing fibers to facilitate the diffusion of the precursor molecules into the fiber pores.
This process for changing the color, tint, or hue of keratin-containing fibers has been successfully used for many years; however, the presence of the oxidative catalyst also provides a means for damaging the keratin polymers themselves. Repeated exposure to the oxidative catalysts contained in dyeing compositions can lead to a cumulative breakdown of the keratin-containing fibers. As a remedy, post oxidative dyeing compositions such as shampoos and conditioners have been developed in an attempt to restore the original hair fiber properties. One drawback to these compositions is that they can simply coat the outside of the keratin-containing fibers thereby providing a “masking” of the actual fiber damage. The use of cleansing, conditioning, and maintenance compositions that are ineffective in repairing fiber damage can provide a desirable texture without actually repairing or fortifying the damaged fibers.
Therefore, there is a long felt need for compositions that can be applied to keratin-containing fibers damaged by exposure to oxidative catalysts to restore the fibers to their original pre-treatment conditions. In addition, there is a long felt need for compositions which can provide protection against further damage to fibers while providing effective cleaning and conditioning of the fibers.